Chapter 9 Tables, Note 9

Individual insulated conductor assemblies are not considered a cable when calculating raceway fill.
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Individual insulated conductor assemblies are not considered a cable when calculating raceway fill.

Code Change Summary: Chapter 9, Note 9 was expanded to clarify the rules on calculating cables in a conduit or raceway.

Chapter 9, Note 9 previously stated that multiconductor cable, optical fiber cable, or flexible cord of two or more conductors is treated as a single conductor for calculating the percentage of conduit or tubing fill area. For cables that have elliptical cross sections (such as NM cable), the cross-sectional area calculation is based on using the major diameter of the ellipse as a circle diameter.

In the 2017 NEC, additional language was inserted to address other configurations of conductor assemblies in a conduit or raceway. Now, assemblies of single insulated conductors without an overall covering are not considered as a cable when determining conduit or tubing fill area. The conduit or tubing fill for the assemblies is calculated based upon the individual conductors.

The issue behind the code change is a newer practice of twisting individual conductors together and then placing the assembly on one reel for shipping and installation. These conductors have been mistakenly thought of as a cable when it comes to figuring the amount of raceway fill. The new code change makes it clear that they cannot be considered as a cable but are counted individually when determining raceway fill.

Below is a preview of the NEC. See the actual NEC text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC edition of NFPA 70.

2014 Code Language:

Chapter 9 Notes to Tables

(9) A multiconductor cable, optical fiber cable, or flexible cord of two or more conductors shall be treated as a single conductor for calculating percentage conduit fill area. For cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter.

2017 Code Language:

Chapter 9 Notes to Tables

(9) A multiconductor cable, optical fiber cable, or flexible cord of two or more conductors shall be treated as a single conductor for calculating percentage conduit or tubing fill area. For cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter. Assemblies of single insulated conductors without an overall covering shall not be considered a cable when determining conduit or tubing fill area. The conduit or tubing fill for the assemblies shall be calculated based upon the individual conductors.

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Chapter 9 Tables, Note 9

Below is a Real Question from our Electrical Continuing Education Courses for Electrical License Renewal:

Which of the following is true when determining raceway fill?

A: Twisted individual conductor assemblies are considered as an individual cable.
B: Each individual insulated conductor in a twisted conductor assembly is counted individually.
C: Calculations for cables with elliptical cross sections shall be based on using the minor diameter of the ellipse as a circle diameter.
D: Calculations for conductors with elliptical surfaces shall be based on using the minor diameter of the ellipse as a circle diameter.
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